Aromatic hydrocarbons, such as benzene, toluene and xylenes (“BTX”), serve as important building blocks for a variety of plastics, foams and fibers. Traditionally, these compounds have been produced via catalytic reformation of naphtha or through steam cracking of naphtha or gas oils, producing streams such as reformate and pyrolysis gasoline. BTX derived from such traditional methods typically include substantial amounts of non-aromatic compounds having similar boiling points. As such, simple distillation or fractionation is not a cost effective or practical method for separation.
Accordingly, liquid-liquid extraction techniques have been used. Such extraction techniques typically use a solvent which exhibits a higher affinity for the aromatic compounds to selectively extract the aromatic compounds from the mixture of aromatics and non-aromatics. For example, one widely used solvent extraction technique is the sulfolane process developed by Shell Oil Company. The process uses a combination of liquid-liquid extraction and extractive distillation in a single, integrated design, and employs tetrahydrothiophene-1,1-dioxide (or sulfolane) as a solvent and water as a co-solvent. In practice, however, the design suffers in that light impurities have a tendency to buildup in the extractive distillation tower and recycle system. This is due to sieve tray fouling or high unit rates, both reducing disengaging times. These undesired effects result in the incapacity of the extractor to efficiently remove and recover the aromatic compounds within the mixed feedstock.
The typical response to correcting the incapacity of the extractor is to move the recycle location, add more stages of sieve trays during a down time, reduce operating rates, or shutdown and clean/replace the sieve tray decks.
There is a need, therefore, for more effective and efficient apparatus and methods for the separation of aromatic hydrocarbons and non-aromatic hydrocarbons.